var canvas, ctx;
var circles = [];
var selectedCircle;
var hoveredCircle;
var button;
var moving = false;
var speed = 2.0;

// -------------------------------------------------------------

// objects :

function Circle(x, y, radius){
  this.x = x;
  this.y = y;
  this.radius = radius;
}

function Button(x, y, w, h, state, image) {
  this.x = x;
  this.y = y;
  this.w = w;
  this.h = h;
  this.state = state;
  this.imageShift = 0;
  this.image = image;
}
// -------------------------------------------------------------

// draw functions :

function clear() { // clear canvas function
  ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height);
}

function drawCircle(ctx, x, y, radius) { // draw circle function
  ctx.fillStyle = 'rgba(255, 35, 55, 1.0)';

  ctx.beginPath();
  ctx.arc(x, y, radius, 0, Math.PI*2, true);
  ctx.closePath();

  ctx.fill();

  ctx.lineWidth = 1;
  ctx.strokeStyle = 'rgba(0, 0, 0, 1.0)';
  ctx.stroke(); // draw border
}

function drawScene() { // main drawScene function
  clear(); // clear canvas

  // draw the title text
  ctx.font = '42px DS-Digital';
  ctx.textAlign = 'center';
  ctx.fillStyle = '#ffffff';
  ctx.fillText('Welcome to lesson #2', ctx.canvas.width/2, 50);

  var bg_gradient = ctx.createLinearGradient(0, 200, 0, 400);
  bg_gradient.addColorStop(0.0, 'rgba(255, 0, 0, 0.8)');
  bg_gradient.addColorStop(0.5, 'rgba(0, 255, 0, 0.8)');
  bg_gradient.addColorStop(1.0, 'rgba(0, 0, 255, 0.8)');

  ctx.beginPath(); // custom shape begin
  ctx.fillStyle = bg_gradient;
  ctx.moveTo(circles[0].x, circles[0].y);
  for (var i=0; i<circles.length; i++) {
    ctx.lineTo(circles[i].x, circles[i].y);
  }
  ctx.closePath(); // custom shape end
  ctx.fill(); // fill custom shape

  ctx.lineWidth = 2;
  ctx.strokeStyle = 'rgba(0, 0, 255, 0.5)';
  ctx.stroke(); // draw border

  // reverting direction
  if (circles[0].x <= 300 || circles[0].x >= 385) {
    speed = -speed;
  }

  // central object behavior
  if (moving) {
    circles[0].x -= speed;
    circles[0].y -= speed;
    circles[1].x += speed;
    circles[1].y -= speed;
    circles[2].x += speed;
    circles[2].y += speed;
    circles[3].x -= speed;
    circles[3].y += speed;
  }

  drawCircle(ctx, circles[0].x, circles[0].y, (hoveredCircle == 0) ? 25 : 15);
  drawCircle(ctx, circles[1].x, circles[1].y, (hoveredCircle == 1) ? 25 : 15);
  drawCircle(ctx, circles[2].x, circles[2].y, (hoveredCircle == 2) ? 25 : 15);
  drawCircle(ctx, circles[3].x, circles[3].y, (hoveredCircle == 3) ? 25 : 15);

  // draw button
  ctx.drawImage(button.image, 0, button.imageShift, button.w, button.h, button.x, button.y, button.w, button.h);

  // draw text
  ctx.font = '30px DS-Digital';
  ctx.fillStyle = '#ffffff';
  ctx.fillText('Play/Pause', 135, 480);
  ctx.fillText(button.state, 135, 515);
}

// -------------------------------------------------------------

// initialization

$(function(){
  canvas = document.getElementById('scene');
  ctx = canvas.getContext('2d');

  var circleRadius = 15;
  var width = canvas.width;
  var height = canvas.height;

  // lets add 4 circles manually
  circles.push(new Circle(width / 2 - 20, height / 2 - 20, circleRadius));
  circles.push(new Circle(width / 2 + 20, height / 2 - 20, circleRadius));
  circles.push(new Circle(width / 2 + 20, height / 2 + 20, circleRadius));
  circles.push(new Circle(width / 2 - 20, height / 2 + 20, circleRadius));

  // load the guide sprite image
  buttonImage = new Image();
  buttonImage.src = 'images/button.png';
  buttonImage.onload = function() {
  }
  button = new Button(50, 450, 180, 120, 'normal', buttonImage);

  // binding mousedown event (for dragging)
  $('#scene').mousedown(function(e) {

    var mouseX = e.layerX || 0;
    var mouseY = e.layerY || 0;
    for (var i=0; i<circles.length; i++) { // checking through all circles - are mouse down inside circle or not
      var circleX = circles[i].x;
      var circleY = circles[i].y;
      var radius = circles[i].radius;
      if (Math.pow(mouseX-circleX,2) + Math.pow(mouseY-circleY,2) < Math.pow(radius,2)) {
        selectedCircle = i;
        break;
      }
    }

    // button behavior
    if (mouseX > button.x && mouseX < button.x+button.w && mouseY > button.y && mouseY < button.y+button.h) {
      button.state = 'pressed';
      button.imageShift = 262;
    }
  });

  $('#scene').mousemove(function(e) { // binding mousemove event for dragging selected circle
    var mouseX = e.layerX || 0;
    var mouseY = e.layerY || 0;
    if (selectedCircle != undefined) {
      // var canvasPosition = $(this).offset();

      var radius = circles[selectedCircle].radius;
      circles[selectedCircle] = new Circle(mouseX, mouseY,radius); // changing position of selected circle
    }

    hoveredCircle = undefined;
    for (var i=0; i<circles.length; i++) { // checking through all circles - are mouse down inside circle or not
      var circleX = circles[i].x;
      var circleY = circles[i].y;
      var radius = circles[i].radius;

      if (Math.pow(mouseX-circleX,2) + Math.pow(mouseY-circleY,2) < Math.pow(radius,2)) {
        hoveredCircle = i;
        circles[hoveredCircle] = new Circle(circleX, circleY, 25);
        break;
      }
    }

    // button behavior
    if (button.state != 'pressed') {
      button.state = 'normal';
      button.imageShift = 0;
      if (mouseX > button.x && mouseX < button.x+button.w && mouseY > button.y && mouseY < button.y+button.h) {
        button.state = 'hover';
        button.imageShift = 131;
      }
    }
  });

  $('#scene').mouseup(function(e) { // on mouseup - cleaning selectedCircle
    selectedCircle = undefined;

    // button behavior
    if (button.state == 'pressed') {
      moving = !moving;
    }
    button.state = 'normal';
    button.imageShift = 0;
  });

  setInterval(drawScene, 30); // loop drawScene
});